Underground mines must be reinforced by installing large beams to support the ribs and roofs of mine entries and haulageways. These beams are often cumbersome, difficult to handle, and may weigh as much as 300 pounds. Presently, these beams are installed by hand. This process entails lifting a beam weighing up to 500 pounds up to the roof of an entry or haulageway to a horizontal position and then emplacing two or more vertical beams to support the horizontal ceiling beam. Lifting such as this requires intense physical exertion and is quite dangerous to the miners.
Observations of miners installing these underground roof supports led to the idea of developing a simple, reliable, safe, and inexpensive device to reduce the physical labor involved in this process. The device was designed to transport the beam to the desired installation point and then to lift the beam up to a position on the roof such that the necessary support beams can be emplaced underneath. A short report and photograph of such a device is contained in Proceedings - 4th Annual Meeting C.A.M.E., Oct. 1985, p. 120.
General prior art lifting devices include these described in U.S. Pat. Nos. 3,758,076 (Tranchero) and 4,513,950 (Yamagishi). The Tranchero patent describes a mobile, high power hydraulic jack designed to lift motor vehicles. This jack includes a lifting arm mounted on a base frame and is capable of lifting vehicles and transporting them from place to place. The Yamagishi patent also discloses a mobile, hydraulic lifting jack designed to lift vehicles. This jack is pivotally mounted on its frame such that it may rotate 360.degree..